As described in co-pending U.S. patent application Ser. No. 10/629,659 entitled “Dual Polarization Vivaldi Notch/Meander Line Loaded Antenna” by John T. Apostolos, filed on even date herewith, and as described in patent application Ser. No. 10/629,454, entitled “Combined Ultra Wideband Vivaldi: Notch/Meander; Line Loaded Antenna” by John T. Apostolos, filed on even date herewith, both assigned to the assignee hereof and incorporated herein by reference, it is possible to provide an antenna element which is the combination of a Vivaldi notch and a meander line loaded antenna (MLA). These antennas in general have a top horizontal plate surrounded on two sides by downwardly depending plates which form side plates. The side plates are coupled to the horizontal plate through meander lines.
The purpose of providing such a combined Vivaldi notch antenna and meander line loaded antenna, is to take advantage of the high upper frequency cut-off of the Vivaldi notch antenna while establishing a minimized low frequency cut-off by utilizing the meander line loaded antenna configuration. As described in the above patent applications, the operation of these antennas provides continuous grating lobe-free coverage of, for instance, between 50 MHz and 1.5 GHz in a smooth transition between the high frequency cut-off and the low frequency cut-off. Moreover, the Vivaldi notch antennas are provided with a cavity which results in an end-fire configuration. It has been found that antennas combined in this manner produce a single lobe, and are of such a small size that they prevent grating lobes when the antenna elements are arrayed.
Moreover, when the Vivaldi notch, cavity, back facing slot structure is duplicated in the side plate % and a bottom plate to provide a square horn like structure, the antenna can be operated with a number of different switchable polarities, depending on which feed points are used. As a result, with an arrangement of a horn having a top plate, two side plates, and a bottom plate, and feed points at four locations, respectively at the throats of each of the Vivaldi notches, it is possible to provide a horizontal polarization, a vertical polarization, a right hand circular polarization, or a left hand circular polarization. Assuming that the feed points in such a structure are labeled A, B, C, and D, then the following mode table specifies how the various polarizations are established:
VpolHpolRHCpolLHCpolA1011B01−i+iC1011D01−i+i
The result of the inventions in the aforementioned two patent applications is that one can establish an ultra wideband antenna having a single lobe with switchable polarizations.
While the above configurations have a relatively low low frequency cut-off, one needs the opportunity to further decrease the low frequency cut-off down to for instance 20 MHz, so as to provide a super ultra wideband antenna whose operating frequency range goes from 20 MHz to 1.5 GHz and beyond when one can ignore grating lobes.
Such an antenna would be useful in ultra wideband communications and not only for currently authorized ultra wideband commercial applications, but also for military applications which extend from 20 MHz up to multiple gigahertz.